The present invention relates to household refrigerators operating with a vapor compression cycle and more particularly, to refrigerators with a two stage compressor and dual evaporators.
Currently produced household refrigerators operate on the simple vapor compression cycle. The prior art cycle shown in FIG. 1, includes a compressor A, condenser B, expansion valve C, evaporator D, and a two phase refrigerant. In the cycle shown, a capillary tube acts as a throttle. The capillary tube is placed in close proximity with the suction line of the compressor to cool the capillary tube. The subcooling which occurs to the refrigerant in the capillary tube increases the cooling capacity per unit mass flow rate in the system thereby increasing system efficiency which more than compensates for the disadvantage of increasing the temperature of the gas supplied to the compressor. The evaporator in FIG. 1 operates at approximately -10.degree. F. Refrigerator air is blown across the evaporator and the air flow is controlled so that part of the air flow goes to the freezer compartment and the remainder of the flow goes to the fresh food compartment. The refrigerator cycle, therefore, produces its refrigeration effect at a temperature which is appropriate for the freezer, but lower than it needs to be for the fresh food compartment. Since the mechanical energy required to produce cooling at low temperatures is greater than it is at higher temperatures, the simple vapor compression cycle uses more mechanical energy than one which produces cooling at two temperature levels.
A well known procedure to reduce mechanical energy use is to operate two independent refrigeration cycles, one to serve the freezer at low temperatures and one to serve the fresh food compartment at an intermediate temperature. Such a system, however, is very costly.
Another problem which occurs in cooling for freezer operation in the simple vapor compression cycle, is the large temperature difference between the inlet and outlet temperatures of the compressor. The gas exiting the compressor is superheated, which represents a thermodynamic irreversibility which results in a relatively low thermodynamic efficiency. Lowering the amount of superheat will provide for decreased use of mechanical energy and therefore greater efficiency.
It is an object of the present invention to provide a refrigerator system for use in household refrigerators which has improved thermodynamic efficiency.
It is a further object of the present invention to provide a refrigerator system suitable for use in household refrigerators which reduces the gas temperature at the compressor discharge ports.
It is another object of the present invention to provide a refrigerator system which does not have moisture condensing from the air, on the compressor suction lines.